1. Technical Field
The inventive concept relates to a semiconductor device, and more particularly, to a resistive memory device and a fabrication method thereof.
2. Related Art
As typical next-generation memories that replace dynamic random access memories (DRAMs) or flash memories, resistive memory devices have received attentions. The resistive memory devices are memory devices using a variable resistive material that is switched between at least two different resistance states by rapidly changing resistance according to an applied voltage.
As an example of the resistive memories, there are phase-change random access memories (PCRAMs). The PCRAM generally includes a switching element, a lower electrode formed on the switching element, a variable resistive material formed on the lower electrode, and an upper electrode formed on the variable resistive material.
Typically, the PCRAM stores data by changing a crystalline state of the variable resistive material by current applied to the heater. In the PCRAM, the variable resistive material is controlled to have low resistance in a crystalline state and to have high resistance in an amorphous state.
In a write operation, heat generated in the variable resistive material is propagated to peripheral cells. Change in a resistance state in the peripheral cells by the generated heat is called a disturbance phenomenon.
FIGS. 1 and 2 are views illustrating the disturbance phenomenon in the general resistive memory device.
Referring to FIG. 1, a variable resistive material 105 and an upper electrode 109 are formed on an interlayer insulating layer 101 in which heaters 103A, 103B, and 103C are formed.
The crystalline state of the variable resistive material 105 is changed by heat generated in the heaters 103A, 103B, and 103C as access devices (not shown) below the heaters 103A, 103B, and 103C are accessed.
For example, it is assumed that cells positioned on the left heater 103A and the right heater 103B are written with a high resistance (an amorphous state). In this case, the memory cells connected the heaters 103A and 103B have sufficiently amorphized areas 107
At this time, when current is applied to the center heater 103C to write a cell connected to the heater 103C, the heat generated in the variable resistive material 105 by the heater 103C is transferred to adjacent cells and the crystalline states of the variable resistive materials 105 of the cells connected to the heaters 103A and 103B are changed.
Thus, as shown in FIG. 2, the variable resistive material on the heater 103C is normally amorphized (see 111 of FIG. 2), but amorphized areas 107A and 107B of the variable resistive material 105 connected to the heaters 103A and 103B are reduced to reduce resistance of a corresponding cell and thus the written data is distorted.